Early experience plays a critical role in the pathogenesis of inadequate maternal care in primates. In humans, abused and/or neglected female children are likely to become abusive and neglectful mothers. Despite the regularity of the relationship between early rearing and later pathogenesis of maternal behavior, the pathogenic mechanism is not understood. While learning to mother undoubtedly plays a role in the development of adequate maternal care, it is evident that a new parent must be "responsive" and attracted to neonates, but not fearful or indifferent. In many mammals, maternal responsiveness to offspring is hormonally regulated. There is compelling evidence that early social experience alters the development of brain neurotransmitter and neuroendocrine systems in nonhuman primates. We propose to test the hypothesis that differences in early rearing experience provide an etiology for pathogenic maternal behavior by altering brain neuroendocrine and neurotransmitter systems which regulate how the adult perceives and responds to infant stimuli. The study design will elucidate the effects of developmental caregiving experience (DCE) on the development of brain neurotransmitter and neuroendocrine systems, and later parental behavior in the common marmoset monkey. Marmoset juveniles and young adults of both sexes usually assist their mother and father in care of younger siblings and gain DCE. Adult female marmosets that do not have DCE reject or kill their first-born, so the effects of early experience appear to be critical for the later expression of maternal behavior in this primate. We propose to rear marmosets with and without opportunity to gain DCE. Early brain peptidergic and bioamine responses to DCE will be determined. HPA axis, bioamine, peptidergic responses to separation from the natal group, novel environments, and pairing with an adult member of the opposite sex will be determined. Using an operant response paradigm, reward value and biological response to infant visual, auditory, and olfactory cues will be determined prior to and after hormonal priming associated with pregnancy and parturition. The results will enable us to begin to localize brain mechanisms responsible for maternal responsiveness in a primate species, and provide an initial understanding of how these mechanisms contribute to the pathogenic maternal behavior.